1. Field of the Invention
The invention relates to producing a double layer having a hetero-junction which is useful as a storage electrode of an electro-optical camera means and somewhat more particularly to an improved method of producing such a double layer which is characterized by:
(a) a first layer comprised of a transparent semiconductor material having n.sup.+ -conductivity and functioning as an electrically conductive signal electrode; PA1 (b) a second layer composed of a photo-conductive cadmium selenide or cadmium sulfo-selenide having n-conductivity; and PA1 (c) the second layer being produced by vacuum vapor deposition onto the first layer.
2. Prior Art
The manufacture of a so-called hetero-barrier layer target for an electro-optical camera tube is known, for example, from the publication "Fernseh-Und Kino-Technik" (Television and Cinematographic Technology), Vol. 32, No. 9/1978, pages 341-348. This publication suggests, at page 348, that a layer composed of n-conductive cadmium selenide be vacuum vapor-deposited onto a transparent, conductive layer composed of tin oxide. This publication defines a hetero-barrier as being the junction or interface between one or two additionally applied layers to the second layer already mentioned. However, a hetero-junction also exists between a n.sup.+ -conductive tin oxide layer functioning as the signal electrode and a n-conductive semiconductor layer of another material vapor-deposited thereon. Such a junction is necessary to prevent the injection of holes from the signal electrode into the photo-conductive layer or, essentially equivalently, to prevent an electron current in the opposite direction. Both would result in an undesired temperature-dependent dark current, i.e., an electrical signal without light incidence. The dark current and its temperature dependency can be kept very low by the last described hetero-junction in addition to the earlier described hetero barrier-layer in a completed target of a camera tube means.
In order to prevent a camera device from exhibiting image errors in the form of white spots or the like, a homogeneous structure of the photo-conductive layer is required.